Why does one Bowens Prolite 100 flash head sometimes fail to fire with the other?

If one Bowens head fires inconsistently even when you trigger the radio by hand, the camera is probably not the cause. The issue is more likely in the flash, receiver/trigger, sync connection, or settings.

Common things to check:

• power and ready status: make sure the head is fully powered on and recycled
• radio trigger/receiver: weak batteries, channel mismatch, or an unreliable receiver can cause missed fires
• sync cable or connectors: loose or damaged connections often cause intermittent triggering
• optical slave settings: if one head is meant to fire from another, make sure slave mode is enabled and the sensor can “see” the master flash
• test one head at a time: swap heads, cables, and receivers to isolate whether the fault follows the head or the trigger setup
• flash tube/modeling lamp area: a worn tube or internal fault can also cause inconsistent firing

A simple test is to swap the trigger/receiver and sync lead between the working and non-working head. If the problem moves, the trigger or cable is likely at fault. If it stays with the same head, that head may need service.